1. Field of the Invention
The present invention relates to a loudspeaker, and more particularly to a multiple cone type loudspeaker including a plurality of vibrating plates.
2. Description of the Prior Art
Generally, loudspeakers are based on the principle that when a conduction wire in which current flows is under the influence of a certain magnetic field, it is subjected to a physical force to move it. In a loudspeaker of the general type, a voice coil is provided, which serves as the conduction wire in accordance with the above-mentioned principle. To the voice coil, a vibrating plate is attached. When voice current from an amplifier flows in the voice coil, the voice coil moves, thereby causing the vibrating plate to vibrate. As a result, a sound is generated.
Referring to FIG. 1, there is illustrated a double cone type loudspeaker. In the double cone type loudspeaker, a vibrating plate and a sub-cone are moved together by a single voice coil. FIG. 2 is a schematic view for explaining the principle of the double cone type loudspeaker. When the sub-cone denoted by the reference numeral 1' in FIG. 2 moves forwards, a space in the front side of the sub-cone 1' is reduced, thereby increasing the density of air particles 3 existing therein, while a space in the back side of the sub-cone 1' is increased due to the movement of the sub-cone 1', thereby decreasing the density of air therein. By referring to FIG. 2, such a phenomenon can be clearly found. When the sub-cone 1' moves reversely, a phenomenon contrary to that mentioned above occurs.
The variation in the density of air particles 3 generated by the movement of the sub-cone 1' are spread in all directions. As a result, the density of air is almost equalized in both spaces respectively defined at front and back sides of the sub-cone 1' as the vibration of the sub-cone 1' is continued. At a place far apart from the sub-cone 1', a variation in density having little relation the movement of the sub-cone 1' is exhibited. Consequently, the double cone type loudspeaker involves a problem that it exhibits its effect only for a sound of a certain level.